Improve and clarify doc comments for public API

[steindvart]

Problem

Many documentation comments in the go-telegram/bot library lack important details. For example:

• Some comments do not clarify how the function or entity works. For example, WithMiddlewares allows to set middlewares for each incoming request does not specify the order of middleware execution. A more informative comment would be:

  // Set middlewares for each incoming request (update).
  // Middleware functions are called in the order in which they are added.
  

• Comments such as SetWebhook https://core.telegram.org/bots/api#setwebhook should be changed to See Telegram API: https://core.telegram.org/bots/api#setwebhook for clarity and consistency.
• etc.

Proposal

• Add specific details where needed, such as the order of function calls or links to official documentation.
• Use concise language and keep the main point clear.

Arguments

• Clear and informative doc comments help developers use the library correctly and efficiently.